1. FIELD OF THE INVENTION
The present invention relates generally to direct-operated servo valves and, more particularly, to the arrangement of a direct-operated servo valve which is not susceptible to a disturbance such as vibration or impact, which consistently exhibits stable damping characteristics, and which can operate with reduced driving energy.
2. DESCRIPTION OF THE RELATED ART
As disclosed in, for example, Japanese Utility Model Unexamined Publication No. 63-53972, a conventional direct-operated servo valve of this kind adopts a method of damping the motion of a movable part by utilizing the viscous resistance of a viscous fluid charged in the gap between a stator and a movable element.
The method of effect damping by utilizing the viscous resistance of the viscous fluid charged in the gap between the stator and the movable element has been employed as a typical damping method for a direct-operated servo valve since this method is simple and convenient and further realizes the vibration-preventing effect of protecting the movable element from disturbances such as vibration and impact. In other words, since the viscous resistance of the viscous fluid exhibits a damping effect in various directions including the direction of normal motion thereof, if such a viscous fluid is charged in a space surrounding the movable element which has the weakest mechanical strength in the movable part, it is possible to protect the movable element from damage derived from disturbances.
The above method, however, has a number of problems. For example, since the damping force derived from the viscous resistance of the fluid acts directly on the movable element, the damping force acts as a force resisting the driving force generated by the movable element, thereby reducing the driving force correspondingly and increasing the loss of driving energy. In general, this resisting force is proportional to the velocity of the movable element and the viscosity of the fluid, whereas the above method requires a fluid having a relatively large viscosity. As a result, particularly in an arrangement which requires a rapid response, the loss of the driving force excessively increases and the above problem becomes serious. In other words, there are a number of problems such as an increase in the size of a driving means, an increase in driving current, an increase in the amount of heat generated, an increase in the size of a control device, and difficulty in realizing a rapid response.
Also, if the viscosity of the fluid varies with a change in temperature, the damping characteristics also vary, resulting in the characteristics of the control system varying.
Furthermore, since it is necessary to use a fluid having a relatively large viscosity which is difficult to circulate, the heat generated by the driving means tends to be confined in the interior and the temperature easily rises. This leads to the problem that variation in the above characteristics easily occurs.